The present invention relates to methods of winding machines, and in particular, to a method of winding brushless machines.
In AC motors and brushless DC motors the stator winding typically carries multiphase AC current to generate a rotating magnetic field. The most common stator winding arrangement is a three-phase winding, although two-phase windings are common in control systems.
In practice, stator windings typically consist of one or more phases, with each phase consisting of a number of full pitch or fractional pitch coils having one or more turns. In a three-phase stator winding, or any multi-phase stator winding, a separate winding is applied for each phase. Thus, for a two turn stator winding, each phase winding will have two turns.
For good motor performance it is desirable to have a good balance of inductance between the various phase windings. Having a good balance of inductance between phases reduces circulating currents in the windings and distributes power demand on the circuitry driving the motor so that the peak power rating of the motor is not limited by any one circuit driving more than its share of the load. Good balance of inductance also allows a net reduction in a motor's winding inductance, thereby allowing the motor to operate at a higher combination of speed and torque.
Currently, there are a number of methods used to wind the stators of brushless motors.
One method requires individual coils to be wound as a first step. The wound coils are then inserted into the slots of the stator core in a manner such that one side of each coil is first inserted all the way around the motor, after which the other side of the coil is inserted. The result is that one side of the coil is in the bottom of a slot while the other side is in the top of a slot. Thus, this winding method can result in a symmetrical winding with a good balance of inductance between phases. However, because the coils must be interconnected by time-consuming soldering or welding, the reliability of the winding is substantially reduced.
An alternative to this method is to continuously wind a series of continuous coils first, rather than a group of individual coils which must be interconnected later. The coils are then inserted into the slots of the stator. Although this winding method eliminates the need for interconnection, nevertheless, the difficulty of handling a string of interconnected coils remains. To simplify the handling of the coils, in practice one string of coils, i.e., one phase of a motor winding, is normally inserted into the stator slots first, with the second and subsequent strings of coils being inserted in sequence. The result is an unsymmetrical winding having inductance imbalance between the phases, and thus, poorer motor performance.
A third method is to hand wire the coils directly into the stator slots so that no interconnections have to be made. Under this method all of the turns for a given phase are wound at one time so that the winding of that phase is completed before another is started. The result again is an unsymmetrical stator winding having inductance imbalance.